Efficient way to check if a given string is equivalent to at least one string in the given set of strings

Question

Given a set of strings, say "String1", "String2",..., "StringN", what is the most efficient way in C++ to determine (return true or false) whether given string s matches any of the strings in the above set?

Can Boost.Regex be used for this task?

Answer 1

std::unordered_set would provide the most efficient look-up (amortized constant time).

#include <unordered_set>
#include <string>
#include <cassert>

int main() {
    std::unordered_set<std::string> s = {"Hello", "Goodbye", "Good morning"};
    assert(s.find("Goodbye") != s.end());
    assert(s.find("Good afternoon") == s.end());
    return 0;
}

Answer 2

You can put all your strings in a std::set and then check if that string is in the set.